2nd gear stutter.

[flakey]

sounds to me exactly like the 2nd gear cog and sixth gear cog (which make 2nd gear) are slipping on each other, I had the same issue on a gsxr750 and it needed 2nd gear cog,6th gear cog and new fork selectors, the 2 cogs are joined by 3 squares on the back of each cog back to back, under extreme load these are slipping then turning a third of a turn and joining back together again resulting in the most furousouis on off on power with no drop in revs, either needs a new gearbox or gearbox rebuild, my gsxr used to 'kick' like this 3 times in the 2nd gear rev range and gradually got worse, apparently it caused by dropping the clutch to wheelie and the gearbox doesnt like the instant load, cost me £540 for a gearbox rebuild which was as cheap as i could get.
kind regards